Jan 24 2014
A look at the core data used in the PLOS Study  debunking the Blood Type Diet (BTD) finds support for the researcher’s conclusions that if your experimental subjects eat potato chips, sandwiches, pizza, ‘beans,’ mac-and-cheese, French Fries and processed meat products while doing 13.7% of the Blood Type Diet, their final cardiometabolic markers will probably not vary much by blood type.
In other words, whilst the PLOS Study may have debunked something, it wasn’t the Blood Type Diet.
Laying aside my initial concerns about the study expressed in the previous blog, many of which were responded to personally by Dr. El-Sohemy, there remains the one over-arching issue: How accurately did the PLOS study model the Blood Type Diet? Despite Dr. El-Sohemy’s extensive response, this was the one point for which he chose to not answer. Since no clarification was forthcoming, I decided to seek out the answer for myself.
This turns out to have been quite easy, since the food values used in the PLOS study were included as a table in an appendix.  From there I simply prepared a spreadsheet with the corresponding values from my book Eat Right For Your Type (ERFYT) and the PLOS Appendix, when a value in the appendix was available, which as you can see by clicking on the link below, was not very often. I then wrote a short program in Perl to run some simple analytical and counting functions.
I started by simply comparing the incidence of values that appear in ERFYT and the corresponding values that appear in the PLOS Study.
The results were even worse than I expected. An enormous number of foods containing values in ERFYT are missing values in the PLOS Appendix. Out of a total of 540 food values available in ERFYT (excluding ‘Herbs,’ ‘Beverages,’ and ‘Teas,’) only 74 (13.7%) show equivalent values in the PLOS Appendix. It’s easy to see the number of foods missing foods from the PLOS appendix in Table 1. They are the large chunks of grey-colored boxes in the table with the label ‘n/v’.
There are also a considerable number (822) of instances of foods containing specific values (being rated as either ‘beneficial’ or ‘avoid’) in ERFYT but having no equivalent values in the PLOS Appendix. In these occurrences, subjects consuming any of these foods would not have had their effects represented in the PLOS study.
In addition, there are no equivalent values in the PLOS Appendix for a large number of the foods (281) for which ERFYT supplies at least two blood type specific values.
Finally, there are a sizable number (77) of foods for which there are values in ERFYT that differ by blood type (i.e being a ‘beneficial’ for one blood type and ‘avoid’ for another) that were not included in the PLOS Appendix. This number is especially pertinent, because a considerable number of foods where variation by blood type might have been expected were not included in the PLOS study. When the non-ERFYT equivalent foods are excluded (see Table 2) the number of foods missing from the PLOS Appendix containing values that vary by blood type is actually greater than the total number of foods included in the PLOS Appendix (74).
Then I looked at the food values used in the PLOS-BTD Study that have no equivalent value in ERFYT.
These results went from bad to ludicrous.
A total of 37 foods are classed in the PLOS Appendix as possessing BTD values despite having no direct representation in ERFYT. This appears to have resulted from study force-fitting foods from the Toronto-modified Willet 196-item semi-quantitative food frequency questionnaire (TMW) into the food framework of the BTD. However, many of these foods are complex combinations of various single ingredients (‘sandwiches’), or entire categories of foods (‘beans’). These ‘lumped categories’ often possess unknown BTD values, or contain individual foods with specific BTD values that contradict the values assigned to the total category by the PLOS authors.
There are several assumptions about the nature of these complex foods which lead to error. For example, ‘mac and cheese’ is listed as ‘neutral’ for blood types A, B, and AB in the PLOS Appendix, despite the fact that the dish is almost universally prepared with processed American cheese, which is clearly indicated in ERFYT as an ‘avoid.’ Pizza is listed as a ‘neutral’ for blood type A, when in fact pizza is almost always prepared with tomato sauce. Tomatoes are clearly indicated as an ‘avoid’ for this blood type. ‘Hamburger’ is listed in the PLOS Study as ‘beneficial’ for type O, despite the fact that hamburgers are universally served on a wheat bun. Wheat is clearly listed as an ‘avoid’ for blood type O in ERFYT.
Many of the PLOS Appendix foods listed in Table 2 are these sorts of lumped categories, including ‘tropical fruits,’ ‘cooked breakfast cereal,’ ‘sandwiches,’ ‘mixed vegetables,’ ‘grains, other,’ ‘beans,’ etc. These generalizations have the effect of negating many of the BTD-specific food values, in particular the blood type specific lectin reactions. For example, the generalized category ‘beans’ are listed as ‘beneficial’ for blood type A in the PLOS Appendix, when in fact lima beans, in particular, contain a known hemagglutinating lectin specific for that blood type. 
In these circumstances, it appears that the PLOS authors chose to stick with the TMW food descriptions and shoe-horn the BTD values into the TMW. This yields a variety of questionable assertions, such as whether a category simplified into ‘beans’ can be given any sort of BTD value at all. In virtually all the instances of the ‘food-lumping’ seen in Table 2, when the TMW ‘food’ is actually split into BTD values the process yields erroneous conclusions. The PLOS Study does not provide any insight into the process used to determine the BTD rating for foods such as ‘mixed vegetables,’ ‘grains, other,’ etc. but the grading system appears quite arbitrary.
It is well-worth wondering how a study with such basic flaws in its design could have survived peer-review. I assume that the reviewers spent adequate time surveying the basic statistical functions used in the study, but I seriously wonder if any of the reviewers took the time to look at just how closely the PLOS study modeled the BTD. It seems improbable that any of them spent time with a copy of Eat Right For Your Type on their laps, cross-referencing its values with the PLOS Appendix. Yet this is perhaps the most basic question to ask of this study: Did it comprehensively model the BTD before reaching its conclusions? A look at the cross-comparision tabular data clearly indicates that it did not. Because of this very basic design flaw, all subsequent analysis and conclusions are moot; they derive from an improper, inaccurate, experimental model.
That the BTD theory is currently unproven by rigorous scientific study is not argued. In time this can be rectified by studies which accurately and comprehensively prove or disprove the hypothesis. Despite the rejoicing in certain circles  the Blood Type Diet/PLOS study by El-Sohemy, et al. is not that study. I call upon the editors of PLOS ONE to consider retracting this study unless they can justify the scientific basis of these concerns.
- Jingzhou Wang,Bibiana García-Bailo,Daiva E. Nielsen, Ahmed El-Sohemy. ABO Genotype, ‘Blood-Type’ Diet and Cardiometabolic Risk Factors. PLOS ONE DOI: 10.1371/journal.pone.0084749
- Peter D’Adamo, Catheine Whitney. Eat Right For Your Type. Penguin-Putnam Publishers 1996
- Appendix S1 of the PLOS Study
- Sikder SK, Kabat EA, Roberts DD, Goldstein IJ. Immunochemical studies on the combining site of the blood group A-specific lima bean lectin.Carbohydr Res. 1986 Aug 15;151:247-60.
- NeuroLogica Blog: Blood Type Diet Disproved